Various types of prostheses are known in the prior art. Numerous prostheses are constituted by a lower plate and an upper plate enclosing a central core. A part of these prostheses enables the upper plate to slide relative to the central core and optionally permits the central core to slide relative to the lower plate. This sliding of the central core relative to the lower plate allows spontaneous positioning of the core in the ideal position to absorb constraints imposed on the prosthesis during movements made by the patient carrying the prosthesis. However, because of the forces from applied constraints, materials utilized and the form of the different pieces constituting the prosthesis, the sliding of the core is often difficult, which causes rapid wear and heightens the risk of ejection of at least a part of the prosthesis to the outside of the spine, and this is not desirable for the patient.
An intervertebral disc prosthesis is provided that allows movement of the different pieces of the prosthesis between one another, but facilitates core sliding.
Intervertebral disc prostheses in accordance with the present invention comprise at least three pieces including a first plate, a second plate and a core that is mobile relative to at least one of the plates. In a preferred embodiment, the core has a curved surface in contact with at least a part of a complementary curved surface of the first plate and a substantially flat surface in contact with at least a part of a substantially flat surface of the second plate, and limit stops situated near the periphery of the second plate and of the core that limit or prevent, without excessive friction, the movements in translation of the core relative to the second plate, along an axis substantially parallel to the substantially flat surfaces, and limit or prevent the movements in rotation of the core relative to the second plate, about an axis substantially perpendicular to the substantially flat surfaces. In a preferred embodiment, the substantially flat surface of the core has at least one dummy hole facilitating sliding of the core relative to the substantially flat surface of the second plate with which it is in contact.
According to another particular feature in an embodiment, the lower surface of the core and the upper surface of the second plate, known as the lower plate, are substantially flat.
According to another particular feature in an embodiment, at least the substantially flat surface of the core is enclosed in a protective shell, whereof the surface in contact with the substantially flat surface of the second plate and with the substantially flat of the core has at least one hole.
According to another particular feature in an embodiment, the protective shell of the core does not cover the limit stops of the core, so as to avoid contact of the protective shell with the limit stop of the second plate.
According to another particular feature in an embodiment, the area of contact of the substantially flat surface of the core or of the protective shell with the substantially flat surface of the second plate and the area of contact of the curved surface of the core with the curved surfaces of the first plate are substantially equal, on both sides of the core.
According to another particular feature in an embodiment, the angle formed by the edges of the hole present at least on the substantially flat surface of the core or of the protective shell of the core is softened to improve the sliding of the core or of the shell on the substantially flat surface of the second plate.
According to another particular feature in an embodiment, the hole present on the substantially flat surface of the core or of the protective shell of the core is prolonged, as far as the periphery of this substantially flat surface, by grooves forming channels via which the interstitial liquid from surrounding tissue can play a lubricating role to improve the sliding of the core on the substantially flat surface of the second plate, when the prosthesis is in place on the patient.
According to another particular feature in an embodiment, the angle formed by the edges of the grooves prolonging the hole as far as the periphery of the substantially flat surface of the core or of the protective shell of the core is softened to improve the sliding of the core or of the shell on the substantially flat surface of the second plate.
According to another particular feature in an embodiment, the core is made of polyethylene.
According to another particular feature in an embodiment, the protective shell of the core is made of metal.
According to another particular feature in an embodiment, the first and second plates are made of metal.
According to another particular feature in an embodiment, the limit stops consist of male structure of the second plate, cooperating with female structure of the core.
According to another particular feature in an embodiment, the core is mobile relative to the first and/or second plates and that a variable angle between the first and second plates depends on the position of the core, an inclination, in any direction at all, of at least the first plate inducing the displacement of the core between the plates and providing freedom of movement for the patient and, at the same time, helping eliminate the positioning defects of the prosthesis.
According to another particular feature in an embodiment, an angle between the upper surface of the upper plate and the lower surface of the lower plate can be imposed either by the fact that the plane means representing the upper and lower surfaces of the core form an angle, or by the fact that the plane means representing the upper and lower surfaces of the first plate and/or of the second plate form an angle, or by restriction of the movements of the core about a position imposing inclination of at least the first plate.
According to another particular feature in an embodiment, the same plates can be assembled with cores of different thicknesses.
According to another particular feature in the embodiment, at least a part of the surface of the first plate is concave and complementary to the surface of the core with which it is in contact.
According to another particular feature in the embodiment, the dimensions of each male structure are slightly less than those of each female structure so as to permit slight clearance between the core and the second plate.
According to another particular feature in the embodiment, the dimensions of each male structure are substantially the same as those of each female structure so as to prevent any clearance between the core and the second plate.
According to another particular feature in the embodiment, the male structure of the second plate are two contact plates situated opposite one another on two edges of the prosthesis, and the female structure of the core are two recesses.
According to another particular feature in the embodiment, the male structure of the second plate are two walls situated opposite one another in the vicinity of two edges of the prosthesis, and in that the female structure of the core are recesses.
According to another particular feature in the embodiment, the male structure of the lower plate are two nibs curved towards the interior of the prosthesis and situated opposite one another on two edges of the prosthesis, and the female structure of the core are two recesses.
According to another particular feature in the embodiment, at least one of the nibs is replaced by a pin equipped with a hole and on which a plate is fixed by means of a dowel penetrating the hole.
According to another particular feature in the embodiment, the lower surface of the lower plate and the upper surface of the upper plate are provided with teeth or notches situated in the vicinity of at least two edges of the prosthesis and oriented so as to prevent sliding of the prosthesis prior to its adhesion to the osseous tissue permitted by a porous biocompatible coating of the surfaces of the plates in contact with the vertebrae.
According to another particular feature in the embodiment, at least the second plate comprises one or more openings in the vicinity of its front side, provided to receive anchoring means of the prosthesis in a vertebra.
According to another particular feature in the embodiment, the openings of the second plate are circular, and in that the anchoring means have the form of a stud.
According to another particular feature in the embodiment, the head of the anchoring means have larger dimensions than the openings of the second plate, the anchoring means being fixed into a vertebra, the second plate is sandwiched in between the head of the anchoring means and said vertebra.
According to another particular feature in the embodiment, the upper plate is bulged on at least a part of its upper surface to adapt to the form of the vertebrae.
Another aim is to propose an insertion device, between two vertebrae, of intervertebral disc prostheses constituted by a lower plate, an upper plate and a mobile core at least relative to the lower plate. It would be advantageous for the prosthesis insertion device between two vertebrae to allow the prosthesis to be kept sterile, to position it facing the opening made by the surgeon between the two vertebrae, to have it enter this opening by translation then to withdraw the device leaving the prosthesis inserted in its opening.
This aim is attained by an insertion device, between two vertebrae, of intervertebral disc prostheses constituted by a first plate, an second plate and a mobile core at least relative to the second plate, characterised in that it comprises a clip whereof the front surface has a form provided to fit the form of the front edge of the prosthesis and whereof at least two edges are equipped with a gripping means.
According to another particular feature in the embodiment, the gripping means present on the clip may be exhibited, for example, as two flexible blades mounted on the lateral edges of the clip and holding the prosthesis by pinching the lateral edges of the upper and lower plates of the prosthesis.
According to another particular feature in the embodiment, the front surface of the clip has a form provided to fit the form of the front edge of the prosthesis, on one hand, owing to its height at least substantially equal to the height of the prosthesis, so as to come into contact with the front edges of each of the plates of the prosthesis and, on the other hand, to at least one groove in at least the median part of the front surface of the clip to likewise come in contact with the front edge of the core which is slightly set back relative to the front edges of the plates.
According to another particular feature in the embodiment, the rear surface of the clip can be pushed by a first end of a rod, known as a guide, equipped with a pusher at its other end and with a limit stop at a variable position along the guide for limiting the length of the sliding of the guide inside a body of a charger equipped with a head in which is arranged a space dimensioned for receiving the prosthesis and the clip, the position of the limit stop on the guide being adjustable such that the prosthesis, held by the clip, exits from the head of the charger and is centred relative to the vertical axis of the two vertebrae between which it must be implanted when the limit stop contacts the body of the charger.
According to another particular feature in the embodiment, the front end of the gripping means of the prosthesis present on at least two edges of the clip is larger than their back end at which the width of the clip is substantially equal to the width of the space in the head of the charger, such that, when the prosthesis and the clip are in the head of the charger, the prosthesis is held firmly by the gripping means of the clip which are then compressed between the prosthesis and the internal wall of the space arranged in the head of the charger and, when the prosthesis exits from the head of the charger, it is held less firmly by the clip, so as to be able to be released therefrom.